The blood tests that are included in the Day Assessment Unit PRECOG guideline, what they measure and what the results mean.
Like blood pressure, and protein in the urine, the blood tests give a window into your body to see if pre-eclampsia is affecting your blood, liver and kidneys. The tests are for platelet count, liver function tests (usually either AST or ALT), serum creatinine (a measure of kidney function) and serum urate (also known as serum uric acid).
There has been a lot of discussion in the medical journals recently about the importance of these different blood tests. As part of the PRECOG work we reviewed all the scientific papers that have looked at whether any of the blood tests predict pre-eclampsia (i.e. become abnormal before hypertension and proteinuria develop) or predict morbidity (i.e. are abnormal before or at the same time that the mother or baby is poorly).
The first conclusion was that although there are hundreds of studies that have been carried out over the years, there arent enough studies using the same methods and the same standards to come to any firm conclusions. For example, there are a lot of studies looking at serum uric acid but very few of them take into account that uric acid varies in a normal pregnancy - getting higher and higher as the pregnancy develops.
It is safe to say though that at the moment none of the blood tests reliably predict pre-eclampsia in someone with either new hypertension or new proteinuria. That means that you cannot guarantee that the blood test result will become abnormal before pre-eclampsia develops. Once pre-eclampsia has developed the blood tests are a useful measure to see how the body is responding, although in many cases they can all remain normal - even in severe pre-eclampsia. Something like a quarter of women with pre-eclampsia have abnormal platelets, a half have abnormal liver enzymes, and three quarters have abnormal serum uric acid.Which means quite a lot of women dont.
So why bother with blood tests before pre-eclampsia has developed??!!! Because, as many of you know, pre-eclampsia is all about the exception that proves the rule. The typically atypical. For example....
HELLP syndrome describes women with a type of pre-eclampsia which includes abnormally high liver enzymes (EL stands for elevated liver enzymes) and abnormally low platelet count (LP stands for low platelets). The H stands for haemolysis. In a study of hundreds of women with HELLP syndrome in America, 30% of women with a very low platelet count had a diastolic blood pressure of less than 90mmHg when they were first admitted and 14% had only a trace or no proteinuria. So taking blood for blood tests in Day Assessment Unit will pick up women with HELLP syndrome who may otherwise slip through the net.
The other reason for taking blood before pre-eclampsia has developed is because knowing how the levels have changed is really important in understanding how the disease is progressing. In particular a decrease in platelets can give a good indication of what is happening and how soon the baby may need to be delivered.
Just to add that the PRECOG guideline - and the info. in this post - was written for women who do not have chronic hypertension or existing kidney disease. For these women the blood tests for pre-eclampsia can also give valuable information on their other conditions and how they are affecting the body.
Different people/ laboratories use different units when they measure substances in the blood/ urine. In the same way that weight can be measured in kilograms, or stones and pounds, the amount of - say - platelets in your blood can be measured in lots of different ways.
So please dont worry if you seem to have a thousand times more, or less, of something than you think you should! The local laboratory that analyses the results will always indicate whether it is a normal result or not, based on the units they use.